1. Field of the Invention
This invention relates to a door opening/closing apparatus for automatically moving a sliding door to close or open an entrance/exit in case of emergency.
2. Description of the Related Art
Heretofore, many door opening/closing apparatuses have been used, in which sliding doors are moved reciprocally to open and close an entrance/exit or the like. In case of emergency, it may be necessary to move sliding doors that are open in the closing direction to close an entrance/exit or the like. Conversely, closed sliding doors may need to be moved in the opening direction to open the entrance/exit or the like.
For example, to prevent intrusion of smoke or the like generated, due to a fire or a similar cause, into other places, it is necessary to move the open sliding doors in the closing direction so as to close the entrance/exit or the like. Conversely, closed sliding doors may have to be opened at an entrance/exit to a building or the like for escapement therefrom in case of fire, power stoppage, etc.
The sliding door, however, is usually manufactured rigidly, and can be considerably heavy. Such a heavy sliding door requires a strong force to cause its manual sliding. This means that it takes a considerable amount of time for a person inside a building, for example, to escape, which is undesirable at the time of power stoppage, or in case of another emergency.
Meanwhile, a uniform tension spring provides uniform spring force and hence provides a constant torque at all times, which is convenient. However, as described above, the sliding door of the automatic door opening/closing apparatus is usually manufactured rigidly, and is considerably heavy, requiring a very strong force to move the door. Meahwhile, the uniform tension spring provides a uniform force at all times. Particularly, the force is insufficient at the time of the start of movement of the sliding door, and there are situations in which the sliding door can not be moved quickly and smoothly.
Further, in the maintenance and inspection of the operating member, there are situations requiring moving only the operating member, without moving the sliding door. As described above, however, it is necessary to increase the spring force of the uniform tension spring, in which case, the operating member, when moved alone, will move quickly, and therefore the operating member, the door, etc. can be damaged by impacts. In fact, damage to the door, etc. by impacts is likely due to quick movement.